This invention relates to magnetic resonance apparatus useful in the visualization and analysis of organic tissues and bodies, and to research into the cause and symptoms of disease, its diagnosis and treatment.
In the use of magnetic resonance imaging (“MRI”) there is a serious problem with interventional procedures. The problem is that the probe cannot be seen, and therefore its location is unknown at the moment before it is to enter the patient. This is one of the most important reasons why MRI has not been used extensively for interventional procedures.
There are many imaging stereotactic devices currently available. Despite the incredible power of existing imaging technologies however, very few procedures are actually done using the existing technology in a routine clinical setting. There are several reasons for the lack of general acceptance of these devices in existing markets.
Most of the systems are expensive, and normally this expense cannot be justified in terms of usage or benefit for the large capital investment required. Physicians and hospitals are generally not prepared in today's economic climate to make a large investment for a system that may only be used intermittently and may become quickly outdated.
Most existing systems are electronic and use optical and computer interfaces. The majority of these systems do not function in a real-time setting, but rather use special post-processed acquired image information. This information is then used to direct the procedure at a different time and place.
Many of the systems are imager proprietary or dependent, so it is possible that only a few units may be able to use a specific technology. Though these systems claim to have very high real-space accuracy, in reality, they have only limited real-space correlation since there is no live (real-time) imaging to confirm the progress of the procedure.
Most stereotactic units are complex and have multiple components. Some of the systems envelop the patient, for example, through the use of head frames that are bolted directly to the skull. If there is any change in the components of such a rigid system at the time and place of the actual intervention, the previously obtained information that forms the basis for the intervention is no longer valid. These systems also rely on gathering many images to direct the operation, rather than needing only a few. Because of this, the process can be very slow, since a large amount of data needs to be acquired to direct the process.
A number of existing stereotactic systems utilize fiducials that are placed on the patient or the stereotactic frame. These are image-conspicuous markers that are seen in the image space and real-space. Utilizing this information, the virtual reality space depicted on the images is fused with the real-space.
There are a number of devices that attach directly to the scanner, but these are generally cumbersome and have not been used extensively.
There are also a few systems that use very limited vector trajectories (of only a few angles). These are of little value since the limited number of approaches they provide to the target may not be enough to address the complicated anatomy, therapeutic devices and goals of a variety of procedures.
Currently there are a number of rapid CT or MRI data acquisition systems available, but they have the disadvantages of being proprietary and of exposing the patient and operator to increased radiation dosage. These CT systems are analogous to fluoroscopy.
There are a few combined CT and fluoroscopic stereotactic systems. These have the potential to be very versatile, but they are complex proprietary systems. There are also a number of open magnet designs, but these are limited by vendor design. Critical information used to direct the procedure or intervention is based on artifacts from the needle or probe rather than on accurate real-time real-space information. The inherent imaging problems created by these artifacts limit the accuracy of these devices. The image quality of the fast imaging systems in general is not as good as routine imaging techniques.
FIG. 1 is a schematic of an enveloping frame that is used for head stereotactic systems of the prior art. The vertical lines 1 of the box represent the vertical struts, the horizontal lines 2 are crossing members used to define the section plane, the angled lines 3 represent cross-members and the sphere 4 is the target. This frame is bolted or rigidly fixed to the patient and then imaged with many sections. The information gathered is used at a later time and place. Without real-time real-space confirmation during the intervention, there is no absolute confirmation that the previously determined plan is actually being correctly implemented.
FIG. 2 is a schematic of an image obtained from such a fixed frame rigid system. The vertical members 1 are seen at the corners of the square, and the cross-members 3 are used to define the slice location and the target 4. There is no intuitive information that an operator can use to confirm that the information is accurate. Typically, a second system is used to actually execute the procedure at a later time with no real-time real-space confirmation of the previously obtained plan.
FIG. 3 shows an example of an MRI image 5 showing the use of a fixed frame stereotactic unit used for head imaging. The head 6 appears in the center of the image, with the target labeled in the left temporal bone. Also visible are the rods 7 (such as horizontal, vertical and cross-members 1, 2 and 3 shown in FIG. 2) surrounding the skull of the patient as a fixed device. The information is acquired by taking multiple images that must be post-processed.
There are a number of limitations to this type of device. The constituent support tubes are necessarily relatively large (in order to support the static arrangement), and thus cause a certain degree of inherent error in the system. The image shown is a single image that provides no real-time information that an operator might use during an image-monitored procedure. Also, a further error factor arises because the tubes are relatively distant from the target site, and the image itself is not without distortion, making the system distortion sensitive. Also, if the subject is moved, the system cannot be readily realigned.
A number of computer-based systems' disadvantages have been mentioned. The most important of these is that they provide no real-time confirmation at the actual time of intervention. All of these systems use specially acquired post-processed images that assume that the virtual reality of the previously obtained imaging information and the true reality at the time of the actual intervention are identical. These systems are expensive, large, and can only be used in select locations.
There remain problems associated with fast, open, and combined technology systems. All are expensive, vendor specific and, as such, are limited to only a few sites. They are such complicated systems that any minor problem can render them useless, for example, if the batteries on an LED stop working. They have limited real-space accuracy since they have problems with partial volume averaging and other imaging artifacts. Using these systems it may be difficult to track more than one device being used at a time.
Accordingly, the criteria for an improved stereotactic device included:    1. Accuracy in the form of mm level control and live image confirmation.    2. Ability to make rapid adjustments (preferably by remote control), and the use of a single image.    3. Flexibility in the form of multiple dimension adjustability, and the accommodation of a wide variety of probes.    4. Intuitive use through clear, non-computer-generated interpretation of electronic image information.    5. Simple construction; a device that may be compact enough to fix the imager on the patient and inexpensively constructed, and may be of disposable materials.    6. Applicability independent of site and imaging device.
Accordingly, there remains a need for relatively inexpensive stereotactic devices that may be used with a wide variety of imaging systems for the performance of varied procedures, and that may be used with any number of invasive devices and techniques.